This invention relates to a single-stage process for the production of polyamines containing aromatic and/or aliphatic primary amino groups and the products of this process.
It is known that aromatic isocyanates can be converted into primary aromatic amines by acid hydrolysis. However, the conversion is far from complete because the amine formed during hydrolysis further reacts with unreacted isocyanate to form the corresponding urea. This further reaction cannot be suppressed even by using excess strong mineral acid. A recent example of such a procedure is described in Japanese Pat. No. 55 007-827.
German Auslegeschrift No. 1,270,046 describes a process for the production of specific primary aromatic amines containing polyalkylene glycol ether segments. In this disclosed process, reaction products of aromatic di- or triisocyanates with polyalkylene glycol ethers and/or polyalkylene glycol thioethers (preferably those having molecular weights of from 400 to 4000) are reacted with secondary or tertiary carbinols. The products of this reaction are subsequently subjected to thermal decomposition at elevated temperatures in an inert solvent (optionally in the presence of acid catalysts). In addition to the high decomposition temperature, this procedure is disadvantageous in that flammable, readily volatile alkenes are formed during the thermal decomposition of the urethanes. Since these alkenes are explosive in admixture with air, safety measures must be taken.
German Auslegeschrift No. 1,694,152 describes the production of prepolymers containing at least two terminal amino groups by reacting hydrazine, aminophenyl ethylamine or other diamines with an NCO-prepolymer of a polyether polyol and polyisocyanate (NCO:NH-ratio=1:1.5 to 1:5). In this disclosed process, unreacted amine must be carefully removed in a separate step because it catalyzes the reaction with polyisocyanates to a considerable extent, thereby leading to short processing times. The amine may also act as a reactant.
Another possible synthesis of polyamines containing urethane groups is described in French Pat. No. 1,415,317. In this prior art process, NCO-prepolymers containing urethane groups are converted with formic acid into N-formyl derivatives which are subsequently hydrolyzed to form terminal aromatic amines. According to German Auslegeschrift No. 1,155,907, the reaction of NCO-prepolymers with sulfamic acid also leads to compounds containing terminal amino groups. Relatively high molecular weight preadducts containing aliphatic, secondary and primary amino groups may be obtained according to German Auslegeschrift No. 1,215,373 by reacting relatively high molecular weight hydroxyl compounds with ammonia under pressure at elevated temperature in the presence of catalysts. U.S. Pat. No. 3,044,989 teaches that such preadducts may be produced by reacting relatively high molecular weight polyhydroxyl compounds with acrylonitrile, followed by catalytic hydrogenation. Relatively high molecular weight compounds containing terminal amino groups and urethane groups may also be obtained by reacting NCO-prepolymers with enamines, aldimines or ketimines containing hydroxyl groups, followed by hydrolysis (German Offenlegungsschrift No. 2,546,536 and U.S. Pat. No. 3,865,791). Another possible synthesis for aromatic polyamines containing urethane and ether groups is the opening of the ring which occurs in the reaction of isatoic acid anhydride and diols. Polyamines of this type are described, for example, in U.S. Pat. No. 4,180,644 and in German Offenlegungsschriften No. 2,019,432; 2,619,840; 2,648,774 and 2,648,825. However, the poor reactivity of such aromatic ester amines is disadvantageous in numerous applications.
Reaction of nitroaryl isocyanates with polyols, followed by reduction of the nitro groups to aromatic amino groups, is also known (U.S. Pat. No. 2,888,439). This process is disadvantageous in that the reduction step is quite expensive.
It is also known that certain heteroaromatic isocyanic acid esters can be converted into heteroaromatic amines by basic hydrolysis. Unfortunately, the hydrolysis conditions described by H. John in J. Prakt. Chemie 130, 314 et seq and 332 et seq (1931) for two specific, heteroaromatic monoisocyanic acid esters are not only totally unsuitable for the conversion of poly-NCO-compounds into aliphatic and/or aromatic amines, they are also dangerous.
Two of our own proposals (see, German Offenlegungsschriften Nos. 2,948,419 and 3,039,600) are multi-stage processes for the production of polyamines by the alkaline hydrolysis of NCO-prepolymers with excess aqueous alkali hydroxides at low temperatures to form carbamates. The carbamates are then acidified with mineral acids or ion exchanger resins in equivalent quantities or in quantities exceeding the quantity of base to decompose the carbamates. The acidified mixture may then be neutralized with a base and the polyamines subsequently isolated.
The above-described processes for the production of polyamines are all complicated. It would therefore be desirable to further simplify production of polyamines in an economically more favorable manner. A significant advantage in this respect would be afforded by a single-stage process as opposed to the customary multi-stage processes. Further advantages would lie in the absence of salts formed so that a filtration step for finely particulate salts would not be required.
Until now, all attempts to obtain satisfactory yields of polyamines by direct hydrolysis of polyisocyanates in a single-stage have been unsuccessful. Instead of the desired hydrolysis products, the products obtained are partially inhomogeneous, do not flow freely and contain urea groups with very few, if any, amino groups. The reason for this may be attributable to the fact that the isocyanate/amine reaction is considerably faster than the isocyanate/water reaction. For this reason, the hydrolysis reaction catalyzed by alkali hydroxides has been carried out at the lowest possible temperatures and the alkali carbamates inevitably formed have been subsequently decomposed by heat treatment or by treatment with an acid.